WinRTAuthorizer UnauthorizedAccessException

I am running into a problem with the WinRTAuthorizer. If the user decides not the go ahead and press the back button saving of the (mostly null) credentials may conflict with loading of the stored credentials file when logging in again and may cause an UnauthorizedAccessException
thrown by this line in LoadCredentialsFromStorageFile:

var credentialsString = await FileIO.ReadTextAsync(credentialsFile);

Took a copy of LinqToTwitter yesterday (sorry, still need to install git) to find where this occurs.

I would at least change WinRTAuthorizer to not try to save credentials that are null anyway.